refactor: add composite (collection_id, deleted_at) index to nfts table

[crnkovic]

Summary

https://app.clickup.com/t/86drc7q7m

Prior to this change, it would take around ~500ms to execute a query to retrieve the popular collections on the /collections page if there are around 1M NFTs in the table. With this index, it's down to ~90ms. And we have much more than 1M NFTs on staging/prod, thus I can see it taking much longer in prod/staging.

It may not be an ideal query, but it's still an improvement.

Checklist

• I checked my UI changes against the design and there are no notable differences
• I checked my UI changes for any responsiveness issues
• I checked my (code) changes for obvious issues, debug statements and commented code
• I opened a corresponding card on Clickup for any remaining TODOs in my code
• I added a short description on how to test this PR (if necessary)
• I added a storybook entry for the component that was added (if necessary)
• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged